1. Technical Field
The present invention relates to an image reading apparatus and an image reading method.
2. Related Art
In the technical field to which the present invention pertains, an original document input system that uses light sources corresponding to three color components is known. For example, an original document input system of the related art controls the lighting-up operations (or in other words, the ON/OFF states) of light emitting diodes (LED), which are light sources corresponding to three color components, by controlling the lighting-up time period, that is, the duration of illumination, of the light-source LEDs in synchronization with start pulses that define the accumulation time period of electric charge. An example of such an original document input system of the related art is described in JP-A-11-55471.
When the related-art original document input system described in JP-A-11-55471 controls the lighting-up operations of the three-color light-source LEDs, it is conceivable to adjust the light amount thereof by varying the lighting-up time period of these three-color LEDs as in a case where, for example, monochrome image scanning is carried out. Generally speaking, it takes a certain length of a pulse rise time period from a point in time at which a voltage is applied to a point in time at which the amount of light reaches a certain ON level. Similarly, it takes a certain length of a pulse fall time period from a point in time at which the application of a voltage is ceased to a point in time at which the amount of light reaches a certain OFF level. For this reason, in the controlling of the lighting-up operations of the three-color light-source LEDs performed by the original document input system of the related art such as one described in JP-A-11-55471, the actual ratio of light amount among these three-color light-source LEDs could deviate from a desired ratio because of the above-explained delay time if the durations of illumination thereof are set without any appropriate technical consideration.